Rhombic dodecahedral Cu2O/Ag-3D Fe3O4 micro-flower composites for water purification under visible light irradiation

Highlights: • The novel Fe₃O₄/Cu₂O/Ag composites were synthesized by the self-assembly and wet chemical method. • The Fe₃O₄/Cu₂O/Ag composites photocatalyst exhibited excellent activity under visible light. • Fe₃O₄/Cu₂O/Ag was magnetic and could be separated magnetically for recycle use. • A possible mechanism for enhancing photocatalytic activity were proposed. -- Abstract: In this study, 3D Fe₃O₄ micro-flowers were synthesized by the self-assembly approach, then rhombic dodecahedral Cu₂O was successfully loaded onto their surface by wet chemical method. Ag nanocrystals were reduced in situ on the surface of Fe₃O₄/Cu₂O composites to prepare novel Fe₃O₄/Cu₂O/Ag composites. The composites were characterized by SEM, TEM, XRD, XPS, VSM and UV–Vis diffuse reflectance spectroscopy. The effect of Ag nanocrystals on the photocatalytic performance of the Fe₃O₄/Cu₂O composites was investigated by the degradation of methyl orange under visible light irradiation, and the Fe₃O₄/Cu₂O/Ag composites showed higher photocatalytic efficiency than the Fe₃O₄/Cu₂O composites. Photoelectrochemical and PL measurements were carried out to investigate the synergistic effect between the semiconductors and Ag nanocrystals and it was confirmed that the Fe₃O₄/Cu₂O/Ag composites effectively inhibited the recombination of electron-hole pairs, thus improving the photocatalytic activity. The fact that the Fe₃O₄/Cu₂O/Ag composites could be magnetically recycled and that they retained more than 90% of their original activity after six repeated experiments indicates, that they show great potential for wastewater treatment applications.